blink.c

int count = 0;

void setup() {
  pinMode(10, OUTPUT);
  pinMode(9, OUTPUT);
  pinMode(8, OUTPUT);
  pinMode(7, OUTPUT);
}

void loop() {
  count++;
  for (int i = 10; i > 6; i--) {
    digitalWrite(i, count++ % 2 ? HIGH : LOW);
  }
  delay(250);
}